Inelastic non-Newtonian flow over heterogeneously slippery surfaces

摘要

In this study, we investigated inelastic non-Newtonian fluid flow over heterogeneously slippery surfaces. First,we simulated the flow of aqueous xanthan gum solutions over a bubble mattress, which is a superhydrophobicsurface consisting of transversely positioned no-slip walls and no-shear gas bubbles. The results reveal thatfor shear-thinning fluids wall slip can be increased significantly, provided that the system is operated in theshear-thinning regime. For a 0.2 wt% xanthan gum solution with a power-law index of n = 0.4, the numericalresults indicate that wall slip can be enhanced 3.2 times when compared to a Newtonian liquid. This enhancementfactor was also predicted from a theoretical analysis, which gave an expression for the maximum slip lengththat can be attained over flat, heterogeneously slippery surfaces. Although this equation was derived for ano-slipo-shear unit length that is much larger than the typical size of the system, we found that it can also beused to predict the enhancement in the regime where the slip length is proportional to the size of the no-shearregion or the bubble width. The results could be coupled to the hydrodynamic development or entrance length ofthe system, as maximum wall slip is only reached when the fluid flow can fully adapt to the no-slip and no-shearconditions at the wall.